Reference voltage sources which are very substantially independent of process fluctuations, fluctuations of the supply voltage and fluctuations of the ambient variables are required nowadays in integrated circuits. Examples of ambient variables that shall be mentioned here include temperature, pressure and the like. Furthermore, high-volume integrated circuits require temperature sensors which detect a value representing the ambient temperature in the circuit and, with the result of this detection, control corresponding compensation circuits or actively control the circuits.
For generating a reference value, for example a reference voltage, which is, in particular, temperature-independent or linearly proportional to the temperature, a multiplicity of circuits and circuit concepts have been disclosed heretofore. One known method for generating a reference value is the principle of compensating for fluctuations that are accumulated in the form of additive disturbance on a reference value. Temperature compensation is often carried out in this case. The reference values are determined in many cases by the prefactor k*T/e, where k is the Boltzmann constant, T is the temperature and e is the elementary charge.
Changes in conductivity of temperature-sensitive components have usually been used heretofore for determining the temperature. Temperature-sensitive components that shall be specified here include metal or semiconductor resistors, PN or tunnel junction of components or bipolar transistors. These conductivities of the components are not absolute quantities. They are subjected to the production tolerances and usually require calibration routines for an accurate temperature measurement. This usually involves a temperature sensor undergoing passes with known temperature cycles and the measured conductivity or the current value corresponding to the temperature being stored. These stored values are compared with the measured values later in order to reconstruct the actual temperature value. At low temperatures, the thermal noise is also used for measuring the temperature in special cases.
All previously known methods for generating a reference value require a correspondingly high supply voltage for suppressing process fluctuations and fluctuations of the supply voltage.